Prior art cartridge heaters, such as is shown in Drugmand U.S. Pat. No. 3,812,580, use a resistance conductor wound about an extruded ceramic core. The ends of the resistance wire extend into longitudinal openings in the core, wherein each makes electrical contact with a bare multi-strand conductor which has been inserted through the openings. The multi-strand conductors exit the core at one end thereby defining terminal ends. This assembly is inserted in the tubular metal sheath with appropriate centering bushings and powdered refractory material. The sheath is then swaged to compact the refracting material.
A similar cartridge heater construction is shown in Simmons U.S. Pat. No. 3,310,769 wherein a core is formed of compacted magnesium oxide. The Simmons cartridge heater assembly is swaged to provide a high density heating element which results in greater heat output.
The cores of the above two patents, are of cylindrical construction and, as described above, have longitudinal openings therethrough for terminating ends of the resistance wire. Such a ceramic core is relatively expensive to produce, thus increasing the total cost of the cartridge heater.
In view of the above, it is desirable to have a cartridge heater with a core which is inexpensive and simple to produce.